I am also trying to set this. Although my understanding is that I can set it in PX4 (linux version), so that I can connect QGC from another machine on same subnet. However I get the error:
pxh> param set MAV_BROADCAST 1
ERROR [param] Parameter MAV_BROADCAST not found.
I am having this issue as well. Running latest stable release of PX4, QGC. Ubuntu 20.04. Can’t set the parameter in px4 nor can I find it in QGC. Any help would be much appreciated!